You could brave the wet and cold and move up here to Scotland. Then you can work out a binding Separation Agreement based on the assets at the date of separation and divorce with consent after a year:silly:
Seriously, perhaps you could put it to her that there's not much point in spending time and money negotiating separation then go through it again for divorce. You could suggest that she petitions using UB and agree between you acceptable reasons. As petitioner she would have the slight advantage of controlling the timing.
Alternatively you could do as she suggests. A formal Separation Agreement in E&W isn't watertight but if it's reasonable and fair, and she's had legal advice, a court would be unlikely to change much in the future.
The other option is to file for divorce regardless of her wishes and risk it being a catalyst for a cycle of provocation and retaliation.
When I said 'Separation Agreement in E&W' I meant in England & Wales as opposed to Scotland, where a separation agreement is different and ties up all the finances and arrangements for children on divorce.
If you go for a Separation Agreement you could negotiate through mediation and take a copy of what is agreed to sol to look over, advise and turn into a legal document. It really is best to get legal advice though, because without it a court could more easily overturn what was agreed.
I seem to remember in our case there was a clause saying I would apply for divorce by consent at a certain point so that there was some assurance that neither of us would change our minds about the reason the marriage broke down, and it was clear who would make the application and when.